Electronic Structure Research Papers - Academia.edu (original) (raw)

Materials with the olivine LixMPO4 structure form an important new class of materials for rechargeable Li batteries. There is significant interest in their electronic properties because of the importance of electronic conductivity in batteries for high rate applications. The density of states of LixMPO4 (x = 0, 1 and M = Fe, Mn) has been determined with the ab initio GGA+U method, appropriate for these correlated electron systems. Computed results are compared with the optical gap of LiFePO4, as measured using UV-Vis-NIR diffuse reflectance spectroscopy. The results obtained from experiment (3.8-4.0 eV) and GGA+U computations (3.7 eV) are in very good agreement. However, standard GGA, without the same level of treatment of electron correlation, is shown to make large errors in predicting the electronic structure. It is argued that olivines are likely to be polaronic conductors with extrinsically determined carrier levels and that their electronic conductivity is therefore not simply related to the band gap.

- by Fei Zhou
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- Materials Engineering, Condensed Matter Physics, Band Gap, Electronic properties
- by Martin Breza
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- Electronic Structure, Hartree fock method, Molecular Structure
- by Sofia Deloudi
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- Engineering, Materials Engineering, Condensed Matter Physics, Quantum Physics

For Abstract see ChemInform Abstract in Full Text.

- by Leonardo Bernasconi
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- Ab initio calculations, Copper, The, Electronic Structure
- by A. Lushchik
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- Geochemistry, Materials Science, Synchrotron Radiation, Electronic Structure

Photoemission spectra taken at room temperature with high energy and angle resolution on Bi2Sr2CaCu2O8 single crystals reveal a band near EF with weak dispersion along lambdaX. It crosses EF at about 1/2 lambdaX and the occupied part becomes visible up to the Brillouin zone boundary in angle-resolved inverse photoemission spectra. Starting for T&gt;Tc with a clear Fermi edge, for T&lt;Tc

- by Recardo Manzke and +1
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- Materials Engineering, Physics, Condensed Matter Physics, Electronic Structure
- by Timothy Stemmler
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- Chemical Engineering, Inorganic Chemistry, Inorganic, Electronic Structure
- by Alexander Boldyrev
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- Engineering, Chemical Physics, Magnesium, Solid State electronic devices

Due to their bandgap engineering capabilities for optoelectronics applications, the study of nano-graphene has been a topic of interest to researchers in recent years. Using a first-principles study based on density functional theory (DFT) and thermal DFT, we investigated the electronic structures and optical properties of bilayer graphene quantum dots (GQDs). The dielectric tensors, absorption spectra, and the refractive indexes of the bilayer GQDs were obtained for both in-plane and out-of-plane polarization. In addition, we calculated the absorption spectra via time-dependent DFT (TD-DFT) in the linear response regime. The TDDFT results show that a blue shift occurs in the absorption spectrum, which is consistent with the experimental results. In this investigation, we consider triangular and hexagonal GQDs of various sizes with zigzag and armchair edges. Our simulations show that unlike monolayer GQDs, for which light absorption for out-of-plane polarization occurs in the ultraviolet wavelength range of 85-250 nm, the out-of-plane polarization light absorption peaks in the bilayer GQDs appear in the near-infrared range of 500-1600 nm, similar to those in bilayer graphene sheets. The out-of-plane polarization light absorption peaks in the near-infrared range make bilayer GQDs suitable for integrated optics and optical communication applications.

- by Donald Nicholson
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- Thermodynamics, Monte Carlo, Parallel Processing, Density-functional theory

The de Haas-van Alphen effect was observed in the underdoped cuprate YBa2Cu3O6.5 via a torque technique in pulsed magnetic fields up to 59 T. Above a field of approximately 30 T the magnetization exhibits clear quantum oscillations with a single frequency of 540 T and a cyclotron mass of 1.76 times the free electron mass, in excellent agreement with previously observed Shubnikov-de Haas oscillations. The oscillations obey the standard Lifshitz-Kosevich formula of Fermi-liquid theory. This thermodynamic observation of quantum oscillations confirms the existence of a well-defined, closed, and coherent, Fermi surface in the pseudogap phase of cuprates.

- by Cyril Jaudet
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- Magnetic field, Band Structure, Physical sciences, Superconductors
- by Alberto Cortijo
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- Transmission Electron Microscopy, Mathematical Sciences, Physical sciences, EPL
- by Anders Hellman
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- Condensed Matter Physics, Quantum Physics, Surface Science, Time-Delay Systems
- by Somnath Bhattacharyya
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- Engineering, Technology, Transport Properties, Physical sciences
- by Noboru Hioka and +2
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- Engineering, Analytical Chemistry, Inorganic Chemistry, Time-dependent density functional theory
- by Sergio E. Ulloa
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- Kondo effect, Molecular Electronics, Physical sciences, Low Energy Buildngs
- by Philippe Sainctavit
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- Geology, Geochemistry, X ray absorption spectroscopy, American
- by Russell Egdell
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- Band Structure, Electronic Structure, Spectrum, Photoemission
- by Genrich Krasko
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- Materials Engineering, Condensed Matter Physics, Electronics, Energy
- by John Huffman
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- The, Electronic Structure, CHEMICAL SCIENCES, Second Order
- by Gerhard H Schadler
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- Electronic Structure
- by Navid Soheilnia
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- Electronic Structure, CHEMICAL SCIENCES
- by Sabre Kais
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- Phase transition, First-Order Logic, Electronic Structure, Symmetry Breaking
- by Seizo Miyata and +1
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- Engineering, X ray absorption spectroscopy, Doping, Activated Carbon

The newly developed full-potential linearized augmented plane wave (LAPW) and local orbitals (lo) based on standard APW methods are briefly introduced, and the structure and magnetic properties of R(Fe, Si)12 compounds (R = Y, Nd) are calculated using the method. The distribution of Si at different sites is analyzed based on total energy of one crystal unit with structure having been optimized. The characters of magnetic moments, total density of states (TDOS) and partial density of states (PDOS) for different crystal sites Si occupies are obtained and analyzed. The results show that the total magnetic moments of RFe10Si2 (R = Y, Nd) are larger than those of RFe10M 2 (M = Ti, V, Cr, Mn, Mo and W) and the hybridization mechanism is seen as follows. Si(8j) reduce the magnetic moments of Fe at three sites, however, Si(8f) mainly reduce the magnetic moments of Fe(8i) and Fe(8j) atoms. The Curie temperature is markedly enhanced by the introduction of Si atoms according to spin fluctuation of DOS at Fermi level.

- by Zhijian Fan
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- Mathematical Sciences, Physical sciences, Magnetic Properties, Electronic Structure

The polarized Cu K-edge X-ray Absorption Near Edge Structure (XANES) of La2CuO4 has been interpreted by the multiple scattering approach. The size of the cluster of neighbouring atoms having good agreement with the XANES experimental data is determined by 45 atoms surrounding the absorbing Cu. The polarized spectra can be predicted in term of a one-electron dipole (Δl=+1) transition Cu 1s→ϵp, probing the unoccupied p-like (l=1) density of states projected on a Cu site with orbital angular momentum ml=0 in the E∥z spectra, and the ml=1 for the E⊤c spectra. Thus we show that the electronic structure of the high energy conduction bands, beyond the Cu 3d band, of La2CuO4 are well described in terms of the one-electron approximation. It is shown that XANES spectra are consistent with the contraction of the Cu-apex oxygen distance with doping.Final state effects induced by the core hole have been indentified: (i) the core transitions take place in the fully relaxed potential, (ii) the satellite at 7 eV above the main K-XANES peak in both polarizations is assigned to a multielectron shake up excitation. Finally the shoulder on the rising absorption edge, present in many Cu compounds and usually assigned to a shake down multi-electron excitation, is shown to be due to a one-electron transition to a state delocalized over a large cluster.

We investigate the electronic structure of carbon nanotubes functionalized by adsorbates anchored with single C-C covalent bonds. We find that, despite the particular adsorbate, a spin moment with a universal value of 1.0 muB\mu_BmuB per molecule is induced at low coverage. Therefore, we propose a mechanism of bonding-induced magnetism at the carbon surface. The adsorption of a single molecule creates a dispersionless defect state at the Fermi energy, which is mainly localized in the carbon wall and presents a small contribution from the adsorbate. This universal spin moment is fairly independent of the coverage as long as all the molecules occupy the same graphenic sublattice. The magnetic coupling between adsorbates is also studied and reveals a key dependence on the graphenic sublattice adsorption site.

- by Elton Santos
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- Engineering, Carbon Nanotube, Single molecule, Physical sciences
- by Michele Ortolani
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- Physical sciences, Terahertz, Electronic Structure, CHEMICAL SCIENCES
- by Muhamad Azizan
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- Condensed Matter Physics, Quantum Physics, Surface Science, Activation Energy
- by Weiguo Yin and +1
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- Functional Analysis, Transition-Metal Oxides, Band Structure, Physical sciences

Electronic structure calculations of cubic SrTiO3 and SrHfO3 are presented. The full-potential linear augmented-plane-wave method is used and exchange-correlation effects are treated by the local-density approximation. The tendency to ferroelectricity of both compounds is explored and compared by displacing the transition metal atom (Ti or Hf) towards one of the oxygens (001 direction). The calculations show that ferroelectricity is favored in SrTiO3 with respect to SrHfO3 and that this fact may be correlated with the degree of hybridization between transition metal d-O p bands as has been found for other related systems. Also a detailed discussion of the calculated electric field gradients is presented.

- by Mohamed Belkhir
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- Physics, Materials Science, Density-functional theory, Structural Stability
- by Peter Heathcote
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- Bacteria, Electron Transport, Electronic Structure, Cations
- by Milan Damnjanovic and +1
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- Density-functional theory, Solid State electronic devices, Physical sciences, Electronic properties
- by Angela Serpe and +1
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- Inorganic Chemistry, Solid State Chemistry, Crystal structure, Band Structure
- by Xabier Lopez and +1
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- Computational Chemistry, Ab initio calculations, Electronic Structure, THEORETICAL AND COMPUTATIONAL CHEMISTRY
- by Georges Calas
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- Geology, Geochemistry, X ray absorption spectroscopy, New Caledonia

Copper sulfide (Cu2-xS) is a class of low-cost, environment friendly p-type semiconductor, where electronic structure and the thus induced optoelectronic properties can be significantly varied through the creation of copper deficiency. To this end, varying composition of Cu2-xS (i.e., Cu2S, Cu1.96S, Cu1.8S, Cu1.8S+ Cu1.6S and CuS) films were grown here by using a low temperature molecular solution based deposition method, following which a wide range of characterization tools were used to understand their microstructure, electronic structure and optoelectronic properties. The hole concentration of these films are found to vary from 3.32 × 1019 cm−3 to 2.54 × 1022 cm−3 as Cu2-xS composition changes from Cu2S to CuS. This is because of the induced Cu deficiency in Cu2-xS films with decreasing Cu/S-molar ratio, which reduced the Cu d-band width in the valence band, thus pushing the Fermi level deep into the valence band. This leads the optical and transport gap to increase from 1.36 eV to 2.23 eV and 1.31 eV to 2.02 eV respectively with increasing copper deficiencies from Cu2S to CuS. Moreover, in this work, both the valence and conduction band edge positions are found to shift negatively with increasing Cu deficiency in these films.

- by Tvarit Patel
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- Band Structure, Electronic Structure, Copper sulfide, Copper Deficiency
- by Abir Bhattacharya
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- Technology, Kinetics, Quantum Mechanics, Chemical
- by Kendall Houk
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- Density-functional theory, Organic, Electronic Structure, CHEMICAL SCIENCES
- by Carl Hampson
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- Electronic Structure, Spectrum
- by Rosalie Hocking
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- Inorganic Chemistry, Organic Chemistry, Organometallics, Electronic Structure
- by Sushil Auluck
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- Materials Engineering, Condensed Matter Physics, Band Structure, Band Gap